The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2

The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction

ExoMars Raman Laser Spectrometer RLS, a tool for the potential recognition of wet target craters on Mars

In the present work, NIR, LIBS, Raman and XRD techniques have been complementarily used to carry out a comprehensive characterization of a terrestrial analogue selected from the Chesapeake Bay Impact Structure (CBIS). The obtained data clearly highlight the key role of Raman spectroscopy in the detection of minor and trace compounds, through which inferences about geological processes occurred in the CBIS can be extrapolated. Beside the use of commercial systems, further Raman analyses were performed by the Raman Laser Spectrometer (RLS) ExoMars Simulator. This instrument represents the most reliable tool to effectively predict the scientific capabilities of the ExoMars/Raman system that will be deployed on Mars in 2021. By emulating the analytical procedures and operational restrictions established by the ExoMars mission rover design, it was proved that the RLS ExoMars Simulator is able to detect the amorphization of quartz, which constitutes an analytical clue of the impact origin of craters. On the other hand, the detection of barite and siderite, compounds crystallizing under hydrothermal conditions, helps to indirectly confirm the presence of water in impact targets. Furthermore, the RLS ExoMars Simulator capability of performing smart molecular mappings was also evaluated. According to the obtained results, the algorithms developed for its operation provide a great analytical advantage over most of the automatic analysis systems employed by commercial Raman instruments, encouraging its application for many additional scientific and commercial purposes

Identification of hydrated silicate minerals on Mars using MRO-CRISM: Geologic context near Nili Fossae and implications for aqueous alteration

The Noachian terrain west of the Isidis basin hosts a diverse collection of alteration minerals in rocks comprising varied geomorphic units within a 100,000 km2 region in and near the Nili Fossae. Prior investigations in this region by the Observatoire pour l'Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) instrument on Mars Express revealed large exposures of both mafic minerals and iron magnesium phyllosilicates in stratigraphic context. Expanding on the discoveries of OMEGA, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO) has found more spatially widespread and mineralogically diverse alteration minerals than previously realized, which represent multiple aqueous environments. Using CRISM near-infrared spectral data, we detail the basis for identification of iron and magnesium smectites (including both nontronite and more Mg-rich varieties), chlorite, prehnite, serpentine, kaolinite, potassium mica (illite or muscovite), hydrated (opaline) silica, the sodium zeolite analcime, and magnesium carbonate. The detection of serpentine and analcime on Mars is reported here for the first time. We detail the geomorphic context of these minerals using data from high-resolution imagers onboard MRO in conjunction with CRISM. We find that the distribution of alteration minerals is not homogeneous; rather, they occur in provinces with distinctive assemblages of alteration minerals. Key findings are (1) a distinctive stratigraphy, in and around the Nili Fossae, of kaolinite and magnesium carbonate in bedrock units always overlying Fe/Mg smectites and (2) evidence for mineral phases and assemblages indicative of low-grade metamorphic or hydrothermal aqueous alteration in cratered terrains. The alteration minerals around the Nili Fossae are more typical of those resulting from neutral to alkaline conditions rather than acidic conditions, which appear to have dominated much of Mars. Moreover, the mineralogic diversity and geologic context of alteration minerals found in the region around the Nili Fossae indicates several episodes of aqueous activity in multiple distinct environments

Phyllosilicate Diversity and Past Aqueous Activity Revealed at Mawrth Vallis, Mars

Observations by the Mars Reconnaissance Orbiter/Compact Reconnaissance Imaging Spectrometer for Mars in the Mawrth Vallis region show several phyllosilicate species, indicating a wide range of past aqueous activity. Iron/magnesium (Fe/Mg)–smectite is observed in light-toned outcrops that probably formed via aqueous alteration of basalt of the ancient cratered terrain. This unit is overlain by rocks rich in hydrated silica, montmorillonite, and kaolinite that may have formed via subsequent leaching of Fe and Mg through extended aqueous events or a change in aqueous chemistry. A spectral feature attributed to an Fe^(2+) phase is present in many locations in the Mawrth Vallis region at the transition from Fe/Mg-smectite to aluminum/silicon (Al/Si)–rich units. Fe^(2+)-bearing materials in terrestrial sediments are typically associated with microorganisms or changes in pH or cations and could be explained here by hydrothermal activity. The stratigraphy of Fe/Mg-smectite overlain by a ferrous phase, hydrated silica, and then Al-phyllosilicates implies a complex aqueous history

Orbital Identification of Carbonate-Bearing Rocks on Mars

Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering, proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

Recent and fossil deposits of dark material in Martian Craters

As a result of weathering and aeolian processes a fine-grained dark material is distributed all over the Martian surface. On crater floors it is frequently accumulated as dunes. Mobile dunes are probably built and shifted by the actual wind fields. If the dune orientation does not coincide with the actual wind fields, the dunes are assumed fossil. We present a comparison between the actual wind fields and the main orientation of the dune formation. The latter was derived from the dune morphology and wind streaks. The aim of this study is to discriminate between recent and fossil forms of dark material dunes. For the analysis, we have selected about 50 craters with occurrences of aeolian dark dunes. The data base for the craters is HRSC-Data, which provides a high spectral diversity. High resolution MOC-images are used to analyze the dune shapes. For the actual wind directions modeled wind fields from the Mars Climate Database (MCD) and wind direction data from the Mars Global Reference Atmospheric Model (MarsGRAM Ver. 2001) are used. The results of both datasets will be compared. Additionally, THEMIS nighttime infrared data are used to get information about the brightness temperature of the dune surface, which closely relates to thermal inertia. Some of the dune fields show a good correlation with the actual wind fields indicating that they might still be active. But others show different wind directions, suggesting fossil forms. This selective mobility and the analysis of the THEMIS-data indicate differences in the surface properties, e.g. consolidation of some dune surfaces

Dark dunes in Martian craters

As a result of weathering and aeolian processes a fine-grained dark material can be found on both Martian hemispheres. It is characterized by a much lower albedo than the surrounding terrain and accumulates in patches and dune fields. Analysis of near infrared spectra from the OMEGA spectrometer yields a higher content of mafic unoxidized minerals such as high and low Ca-pyroxenes and olivine. On impact crater floors, the material is frequently accumulated into barchan or transverse dune fields. HRSC data show that the material is blown into and out of craters, indicating that such depressions can act as traps or as sources. In some cases, dark layers in crater walls with dark streaks running down slope seem to be an additional supply for the dark material. We measured the dune volume using HRSC-DTMs and estimated the total amount of material inside the craters to verify the proportion of the dark layers as a source mechanism for the material inside. So far, no significant relation between crater degradation stage and dune volume could be recognized. Dark streaks extending downwind from the dune on to the surrounding terrain indicate an unconsolidated characteristic of the material and erosion by aeolian scour. However, not every dune suggests a grain release. This poses the question regarding the ages of active dunes, in which some could be "paleo" features. A comparison of modeled wind fields with the morphology related to wind direction suggests that both wind directions do not coincide in every case. For more detailed information concerning the surface properties, we analyzed the night-time brightness temperatures (from THEMIS data) and the thermal inertia (from TES data) of the dune surfaces. If the dune surfaces have warmer brightness temperatures at night with respect to the surrounding, it can be supposed that the surface is consolidated. The dune fields studied show significant differences in night-time brightness temperatures and thermal inertia due to varieties in the physical structure and the grain size of the surface material. The results show that some dune surfaces consist of unconsolidated sandy material that is recently eroded and moved. These dunes are inferred to be active. We assume that dunes with high thermal inertia values, high night-time brightness temperatures and the absence of interaction with the current blowing wind have consolidated surfaces consisting of cemented particles

The mineralogical composition of dark dunes in Martian craters – A global view

A global selection of about 70 impact craters comprising multiple different types of dark material deposits, such as single dunes, huge dune fields or thin sand sheets was chosen for this study. By analyzing the mineralogy of these deposits, we want to examine whether there is any correlation between the mineralogical composition and the geographical location, or the dune surface induration, which was established previous works [1], respectively. For this analysis, MarsExpress-OMEGA spectral data were corrected for solar irradiance and atmospheric absorptions. The mineral detection was done using an IDL routine that applies a rationing technique on corrected data sets. The implemented rationing technique, as well as the spectral parameters (spectral criteria) used for mineral detection, were developed and described in detail by [2]. They include the typical absorption features for every mineral of interest, such as high- and low-calcium pyroxenes, olivine (forsterite and fayalite) and hydrated minerals. We present a global map showing the mineralogical composition of the selected intra-crater dark material occurrences. Besides the well-known mafic mineral composition (pyroxene and olivine), we could assess that most of the dark deposits show strong pyroxene absorptions. The minor part has olivine absorptions, whereas forsterite occurs in most cases. The results show no mineralogical difference between unconsolidated and consolidated dunes. There is also no correlation between the mineralogical composition and the geographical location recognizable. The unoxidized mafic nature of the material indicates that is was not affected by aqueous weathering. Thus, mechanical weathering could be the major process that caused the comminution of the material. In some places, a portion of the dark material shows absorption features of hydrated minerals indicating that the material has partly underlain a chemical alteration process. The hydration might have been caused by the supply of water, e.g. by melting H2O-frost layers. There is no obvious correlation between hydrated minerals and consolidated dune surfaces. However, it is notable that the positive detection of hydrated minerals concentrates in craters located in Arabia Terra and that all of these intra-crater materials show pyroxene absorptions and no olivine features. Although there is no correlation between the detected mineralogical composition and the dune surface induration, it cannot be excluded that the surface consolidation might correlate to any other minerals that could not be detected by OMEGA